VOLCANOES DESTROY AND
VOLCANOES CREATE
What is a Volcano? • Opening in the Earth’s surface where magma
escapes
• The word volcano is derived from the name of Vulcano island off Sicily, which was named after Vulcan the Roman God of Fire
What is Volcanism?
Volcanism describes all the processes associated with the discharge of magma,
hot fluids and gases
Magma or Lava• Molten rock below the surface of the
Earth that rises in volcanic vents is known as magma
• After it erupts from a volcano it is called lava
MagmaCommonly contains some crystals, fragments of
surrounding (un-melted) rocks, and dissolved gases, but it is primarily a liquid composed
principally of oxygen, silicon, aluminum, iron, magnesium, calcium, sodium, potassium,
titanium, and manganese
LAVA Red hot when it pours or blasts out of a vent
but soon changes to dark red, gray, black, or some other color as it cools and solidifies.
Very hot, gas-rich lava containing abundant iron and magnesium is fluid and flows like hot tar, whereas cooler, gas-poor lava high in silicon, sodium, and potassium flows sluggishly, like thick honey in some cases or in others like
pasty, blocky masses
List any contributions made by Volcanoes
1. Played a key role in forming and modifying the planet
2. More than 80 percent of the Earth's surface--above and below sea level--is of volcanic origin
Contributions 3. Gaseous emissions from volcanic vents over
hundreds of millions of years formed the Earth's earliest oceans and atmosphere
4. Volcanic eruptions have produced mountains, plateaus, and plains, which subsequent erosion and weathering have sculpted into majestic landscapes and formed fertile soils
Where do most volcanoes form?
PLATE BOUNDRIES
MAP LEGEND
World map• plate boundaries (blue lines), • the distribution of recent earthquakes (yellow dots)• active volcanoes (red triangles)
Courtesy of NASA
Review
• Tectonic plates are composed of huge pieces of the lithosphere, (earth’s crust) that are driven by convection currents in the mantle.
• 3 types of plate boundaries; Convergent, Divergent and Transform
Divergent Volcanism • Occurs at mid-oceanic
ridges• As the plates are
pulled apart pillows of lava form new ocean floor
• Non explosive with large amounts of lava
• About 2/3 of volcanism occurs underwater @ divergent boundries
Convergent Volcanism
• Oceanic-oceanic subduction zone • Produce a line of volcanoes parallel to the oceanic
trench, • The chain of volcanoes is called an island arc• For Example the Aleutian Island chain
Convergent Volcanism
• Oceanic-continental subduction zone • Belt of volcanoes will be generated on continental
crust• The belt is then called a volcanic arc• Characterized by explosive eruptions • For Example the U.S. Pacific northwest, and the
Andes of South America and the most volcanically active belt on Earth is known as the Ring of Fire
452 active and dormant volcanoes
Hot Spots
Hot spots: Regions inside a plate with active volcanism
• Unlike other volcanoes, not created at plate boundaries, created within the plate interiors• For Example The Hawaiian Islands
ANY QUESTIONS?